Class 10 — Magnetic Effects of Current

Chapter Overview & Weightage

“Magnetic Effects of Electric Current” is one of the most scoring chapters in Class 10 Science. Every CBSE board paper has at least one question, and over the past five years it has consistently delivered 5–7 marks. The concepts are visual and rule-based — once you’ve understood the right-hand thumb rule and Fleming’s left-hand rule, half the chapter is done.

Key Concepts You Must Know

Ranked by board frequency:

• Magnetic field around a straight current-carrying conductor — concentric circles, direction by right-hand thumb rule.
• Field due to circular loop — at the centre, perpendicular to the plane.
• Field due to a solenoid — uniform inside, like a bar magnet outside. Polarity by right-hand rule.
• Force on a current-carrying conductor in a magnetic field — Fleming’s left-hand rule.
• DC Motor — converts electrical to mechanical energy. Split-ring commutator reverses current every half-rotation.
• Electromagnetic induction — moving a magnet near a coil induces EMF (Faraday’s law, qualitative at Class 10).
• AC Generator — slip rings, sinusoidal output. Compare and contrast with DC motor.
• Domestic electric circuit — live, neutral, earth wires; fuse, MCB, short-circuit and overloading.

Important Formulas

Class 10 doesn’t require numerical use of $\mu_0$ or detailed Biot-Savart. Focus on the qualitative relationships and rule-application.

Solved Previous Year Questions

PYQ 1 — Direction of Magnetic Field (CBSE 2023, 2 marks)

Q. A vertical wire carries current upward. Find the direction of the magnetic field at a point (a) east of the wire, (b) west of the wire.

Solution. Use the right-hand thumb rule: thumb points up (along current), fingers curl in the direction of $B$. At east — $B$ points northward (out of the page if we’re looking down). At west — $B$ points southward.

(In CBSE’s convention: at east of an upward current, $B$ points “into the page” of north; at west, $B$ points “out of the page” of south. The visual is the key — draw the wire with arrow up and concentric circles around it.)

PYQ 2 — DC Motor (CBSE 2022, 5 marks)

Q. Draw a labelled diagram of a DC motor and explain its working. Why is a split-ring commutator essential?

Solution. A DC motor has: (1) armature coil, (2) strong horseshoe magnet (poles N, S), (3) split-ring commutator, (4) brushes, (5) battery.

When current passes through the coil in the magnetic field, the two arms of the coil experience equal and opposite forces (Fleming’s left-hand rule), creating a torque that rotates the coil. After a half-rotation, the split-ring reverses the current direction in the coil — keeping the torque always in the same rotational sense. Without the commutator, the coil would oscillate back and forth instead of rotating continuously.

PYQ 3 — Right-hand thumb rule (CBSE 2024, 3 marks)

Q. Two parallel wires carry currents in the same direction. State whether they attract or repel, and explain.

Solution. Each wire’s magnetic field at the location of the other points in the direction given by the right-hand thumb rule. Applying Fleming’s left-hand rule on each wire (current and field), the force on each is toward the other. They attract.

If the currents were antiparallel, the forces would reverse and they would repel. This is the basis for the Ampere unit definition.

Difficulty Distribution

For this chapter:

• Easy (40%): Right-hand thumb rule applications, identifying poles of solenoid, naming components of motor/generator.
• Medium (45%): Fleming’s left-hand rule problems, comparing AC and DC, domestic circuit safety, working of DC motor.
• Hard (15%): Numerical involving forces on conductors (uncommon in Class 10), conceptual MCQs distinguishing induced EMF from current.

Time allocation: 45 min for the entire chapter in one sitting is reasonable.

Expert Strategy

Common Traps